If you hadn't had much to eat it could have been a low blood sugar episode. I get them quite often as a rare complication post op, hypoglycaemic episodes. They start with weakness in my arms and legs, then a general lethargy, dizziness, butterflies in my tummy, heavy limbs and then nausea. Easily solved by some fast release sugar (chocolate!) followed by something carby for a slow release sustain.
We do react to meds differently post op, I am now allergic to penicillin, and react to codeine, but I am fine with Tramadol and paracetemol. Paracetemol with aspirin/caffiene is a very mild med to react to though. The amount of caffiene in them isn't huge, do you drink coffee ever?